Automatic memory management automatically manages the memory-related parameters for both Oracle ASM and database instances with the MEMORY_TARGET parameter. Automatic memory management is enabled by default on an Oracle ASM instance, even when the MEMORY_TARGET parameter is not explicitly set. The default value used for MEMORY_TARGET is acceptable for most environments. This is the only parameter that you must set for complete Oracle ASM memory management. Oracle strongly recommends that you use automatic memory management for Oracle ASM.
If you do not set a value for MEMORY_TARGET, but you do set values for other memory related parameters, Oracle internally calculates the optimum value for MEMORY_TARGET based on those memory parameter values. You can also increase MEMORY_TARGET dynamically, up to the value of the MEMORY_MAX_TARGET parameter, just as you can do for the database instance.
Although it is not recommended, you can disable automatic memory management by either setting the value for MEMORY_TARGET to 0 in the Oracle ASM parameter file or by running an ALTER SYSTEM SET MEMORY_TARGET=0 statement. When you disable automatic memory management, Oracle reverts to automatic shared memory management and automatic PGA memory management. To revert to Oracle Database 10g Release 2 (10.2) functionality to manually manage Oracle ASM SGA memory, also run the ALTER SYSTEM SET SGA_TARGET=0 statement. Unless specified, the behaviors of the automatic memory management parameters in Oracle ASM instances behave the same as in Oracle Database instances.
For a Linux environment, automatic memory management cannot work if /dev/shm is not available or is undersized. For more information, see Oracle Database Administrator's Reference for Linux and UNIX-Based Operating Systems. For information about platforms that support automatic memory management, see Oracle Database Administrator's Guide.
The minimum MEMORY_TARGET for Oracle ASM is 1 GB. If you set MEMORY_TARGET lower, then Oracle increases the value for MEMORY_TARGET to 1 GB automatically.
For the recommended settings of memory initialization parameters in an Oracle Exadata environment, refer to the Oracle Exadata documentation.
Oracle Database Administrator's Guide for more information about the functionality of automatic memory management for database instances, which varies from Oracle ASM
Oracle Database Concepts for an overview of memory management methods